Make it so

May 3, 2015

Who needs reaction mass? And who understands the physics behind this?

I ran across a mention of testing an EM drive in vacuum a couple of weeks ago but didn’t pay it much attention because of where I found it. Then Paul sent a link to this article at a NASA site which makes me take it more seriously.

If you’re interested in space flight, RTWT. It could be a game-changer.

A group at NASA’s Johnson Space Center has successfully tested an electromagnetic (EM) propulsion drive in a vacuum – a major breakthrough for a multi-year international effort comprising several competing research teams. Thrust measurements of the EM Drive defy classical physics’ expectations that such a closed (microwave) cavity should be unusable for space propulsion because of the law of conservation of momentum.

EM Drive:

Last summer, NASA Eagleworks – an advanced propulsion research group led by Dr. Harold “Sonny” White at the Johnson Space Center (JSC) – made waves throughout the scientific and technical communities when the group presented their test results on July 28-30, 2014, at the 50th AIAA/ASME/SAE/ASEE Joint Propulsion Conference in Cleveland, Ohio.

Those results related to experimental testing of an EM Drive – a concept that originated around 2001 when a small UK company, Satellite Propulsion Research Ltd (SPR), under Roger J. Shawyer, started a Research and Development (R&D) program.

The concept of an EM Drive as put forth by SPR was that electromagnetic microwave cavities might provide for the direct conversion of electrical energy to thrust without the need to expel any propellant.

This lack of expulsion of propellant from the drive was met with initial skepticism within the scientific community because this lack of propellant expulsion would leave nothing to balance the change in the spacecraft’s momentum if it were able to accelerate.

What amazes me (and apparently many others) is that you don’t need to haul along a bunch of reaction mass to throw away behind you in order to accelerate.

Heinlein wrote an article about interplanetary travel at constant acceleration. (He and many others have written novels based on that assumption, of course.) The travel times are remarkably shorter than building up an initial velocity and then coasting – which is how we do it now. The critical factor in using constant acceleration has always been carrying the reaction mass you needed to expel in order to get the acceleration.

Even a constant acceleration of 0.1G (0.98m/sec2) makes a huge difference in travel time.

And now – maybe – that’s not necessary after all? Wow. I don’t know if Larry Niven would classify this as an example of his reaction-less drive but I think it’s pretty close.